DE 40 20 780 C1 (U.S. Pat. No. 5,409,771 A) discloses the post-treatment of superabsorbent polymers by post-crosslinking the surfaces of the polymer particles. The post-crosslinking of the surface of the water-absorbing polymer particles particularly increases the absorption capacity of the polymer particles under pressure.
DE 199 09 653 A1 (US 2003/207997 A1) and DE 199 09 838 A1 (U.S. Pat. No. 6,605,673 B1) describe pulverulent, surface post-cross-linked polymers which absorb water, aqueous or serous fluids or blood, which are based on monomers bearing acid groups and which have been coated and post-cross-linked with a surface post-crosslinker and a cation in aqueous solution. The polymers disclosed in this prior art have advantageous absorption properties compared to conventional polymers, especially a high permeability.
Hygiene articles such as diapers and incontinent pads, liners and articles containing superabsorbent polymers are designed to absorb bodily fluids such as urine. Urine can generally be a source of two major types of nuisance malodors; one from the bacterial or enzymatic decomposition of urea to form ammonia; the second from organic molecules found in the urine itself. The first odor requires time to develop, i.e. time for the urea to decompose to ammonia, depending on many factors such as the bacteria present on the skin, the pH, the temperature, among others. Odor from organic molecules, usually the byproducts of digestion or other metabolic processes, on the other hand, is present immediately when the urine is excreted from the body. There is a need for a means of controlling, reducing or even eliminating both types of odor.
In the case of prolonged wearing of hygiene articles including absorbent polymers, especially when some of these have already absorbed body fluids such as urine, the organic constituents of the urine and the body heat of the wearer can soon cause an unpleasant odor nuisance. In order to counter this, numerous attempts have been made through appropriate additions in the non-superabsorbent constituents of the hygiene article to achieve binding of the odor-forming substances or to mask the odor by means of perfume or the like. The introduction of such substances in the form of non-superabsorbent constituents often has an adverse effect on the performance of these hygiene articles during wear. For instance, the odor-inhibiting or odor-reducing substances, which are at first spatially separate from the superabsorbent region, may be brought into the region which contains superabsorbent by the introduction of bodily fluids, for example by a washing action, odor where they then exhibit an adverse effect overall on the performance of the superabsorbent and hence of the hygiene article. A further disadvantage of this concept is that the majority of the body fluid released into the hygiene article is in any case present within the superabsorbent, and the odor-inhibiting or odor-reducing substances present outside the superabsorbent are therefore less able to display their effect.
DE 198 25 486 (US 2004/157989 A1) and DE 199 39 662 A1 (US 2003/157318 A1) disclose the combination of superabsorbents with cyclodextrin for odor reduction. However, it can be inferred from this approach, which is indeed promising, that the cyclodextrin exhibits its odor-inhibiting action in the superabsorbent only under particular conditions, namely when it is ensured that the cyclodextrin does not separate again from the superabsorbent. It is preferable in this context that the cyclodextrin is incorporated at least into the surface of the superabsorbent article, by virtue of cyclodextrin and/or cyclodextrin derivatives being covalently and/or ionically bonded and/or incorporated therein.
DE 103 34 271 (US 2007/015860 A1) further discloses superabsorbent agglomerates which may have a multitude of odor binders in homogeneous form in the agglomerate. However, this document, which discloses an excellent solution for the use of fine superabsorbent particles, does not provide superabsorbents having odor-binding properties which are of particularly good suitability for use in hygiene articles. Thus, as well as an efficient and effective use of the odor binders, the superabsorbent properties influenced by this odor binders are also still in need of improvement.
DE-A-10 2005 055 497 (US 2010/035757 A1) teaches imparting improved odor-binding properties to superabsorbent polymers by contacting with metal salts of ricinoleic acid and/or with amino acids.
Other approaches such as the use of lower pH additives, enzyme inhibitors, chelants and the like, are only effective in delaying the formation of ammonia from urea and have little effect on organic molecule odor, or only address a small fraction of the types of organic odor. One of the difficulties with controlling, reducing or eliminating organic odor is the large variety of chemistries of the organic malodor molecules, including ketones and aldehydes, amines, mercaptans, sulfides, cyclic compounds, unsaturated compounds and aromatics and the like. Only addressing one or two classes of organic odor does little to reduce the overall nuisance created by urine malodors.